Oil pumping out of engine

[muskrat]

G'day Trevor.
Yes I've been guilty of that. When I got my 51 A7 in 1981 after it had sat in a chook shed for 15 years. "Ah, no oil in the tank, better top up before I try starting it" 
We're lucky to have a sump plate. If the HD wet sumps it's all over the floor! DAMHIK
Cheers

[ChrisW]

So what's the best oil for my Dad's bike, given that it won't be ridden much and only started occasionally.
The Haynes manual recommends Castrol GTX 20W/50.

Chris

[muskrat]

G'day Chris.
  Oh no an oil thread 
Originally a mono grade oil was used eg sae 30 or 50. That type of oil doesn't carry the impurities away and is "filtered" out in the sludge trap in the crankshaft. This means every 50,000 miles the motor is stripped and the sludge trap is cleaned out.
If an external (spin on filter like a car) filter is used a multi grade 20/50 oil is used as it carries the impurities to the filter.
For Dad's bike with no filter and only run on occasions I'd stick with the mono 30 weight. https://tinyurl.com/yc5m8xwb
Cheers

[ChrisW]

Thanks for that, 30 grade it is.

Chris